Distribution networks and fiber components

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Distribution networks and fiber components

• Subject Optical communications
• Chapter 9
• Speaker Duc-Dung Do
• 24th, May, 2004

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Contents

• Distribution networks
• Directional couplers
• Star couplers
• Switches
• Fiber optical isolator
• Wavelength division multiplexing
• Fiber Bragg gratings
• And others (Attenuator, Circulator, Polarization
  Controller)

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Distribution networks
Directional coupler
Favored port
Input port
Tap port
Isolated port

• Throughput loss
• Tap loss

• Directionality
• Excess loss

• Splitting ratio

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Distribution networks
Directional coupler

• If the coupler is lossless then
• and

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Distribution networks
Duplexing network
DC Directional Coupler T Transmitter R Receiver
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Distribution networks
Tee network

• Advantages
• Require less fiber than other do (useful for
  systems covering a large area)
• Disadvantages
• Losses increase linearly with the number of
  terminals.
• Receiver must have a wide dynamic range

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Distribution networks
Tee network

• Total loss
• Without connector loss
• With connector loss

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Distribution networks
Star network

• Advantages
• Losses increase slowly with the number of
  terminals.
• Received power does not change when a different
  terminal transmit.
• Disadvantages
• Require more fiber than Tee network does (used
  for systems covering a small area)

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Distribution networks
Ring network

• Advantages
• No sharing of the optical power by several
  stations (more terminals can be interconnected in
  the network)
• Disadvantages
• More complex than the tee and star networks

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Distribution networks
Ring network

• Basic network
• Normal operation Reconfigured when node 4
  has failed

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Distribution networks
Hybrid Distribution Systems
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Distribution networks
Multifiber Systems
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Directional couplers
Fused biconically tapered directional coupler
Fibers are twisted around one another and put
under tension The junction is heated, softening
the fibers and causing their claddings to fuse
Coupling coefficient
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Directional couplers
Other types of amplitude-division device
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Directional couplers
Other types of wavefront-division device
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Star couplers
Passive star coupler
Active star coupler
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Switches

• Function reroute the optic signals.
• Application Used in distribution networks,
  measuring equipment, and experiments
• Typical device types two-position switch and
  bypass switch

If the switch is set for coupling to port 2 then
Insertion loss (IL)
Crosstalk (CT)
Reproducibility achieving the same insertion
loss each tie the switch is returned to the same
position.
Switching speed how fast the switch can change
from one position to the other
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Switches
Two-position switch
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Switches
Bypass switch
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Fiber optical isolator
Principle
Return loss
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Wavelength-division multiplexing
Principle

• Several channels of information each having a
  different carrier wavelength can be transmitted
  simultaneously over a single fiber
• Important properties Insertion loss, crosstalk,
  uniformity

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Wavelength-division multiplexing
Wavelength-division multiplexed network

• Three channel WDM network

• Full-duplex network

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Wavelength-division multiplexing
Multiplexer/Demultiplexer

• Angular dispersion

• Optical filtering

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Fiber Bragg gratings

• Fiber gratings are a periodic variation in the
  refractive index of the core as measured along
  its axis

• The reflected wavelength obeys Braggs law

• Applications
• 1. Filters for WDM systems
• 2. Wavelength-selective mirrors for fiber laser
• 3. Wavelength stabilization of laser diodes
• 4. Strain and temperature measurements in
  composite fiber optic sensors
• 5. Dispersion compensation
• 6. Gain stabilization and equalization in
  Erbium-doped fiber amplifiers
• 7. Fixed filters
• 8. Tunable filters

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Fiber Bragg gratings
WDM filter Multiplexer/Demultiplexer
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Other components
Attenuator

• Using an absorbing wheel

• Using movable offset fibers

Circulator
Polarization controller
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Summary
Several alternative network architectures
available, such as the tee, star, ring, and a
hybrid combination of basic architectures are
presented Many system components (directional
couplers, transmission star couplers, reflection
star couplers, switches, and multiplexers/demultip
lexers, fiber Bragg grating, and others) are also
available. Fibers are not only commercially
applied on a large scale to unidirectional,
point-to-point telephone links but also in
complex systems that require elaborate
distribution of the optic signals.